Various considerations have been made on a battery comprising a PTC element preventing heat generation in the battery resulting from an excess current at the time of a short circuit for the purpose of improving the safety of the battery.
For example, the surface of a negative electrode current collector is coated with an electronic conductor containing mainly polyethylene and having a PTC function, but the electronic conductor coated on the surface of the negative electrode current collector tends to be decomposed by an alkaline electrolyte, and there may be cases where the PTC function is not sufficiently exhibited.
Further, in another example, a sealing body comprising a PTC element is used in an alkaline battery or a lithium battery. The PTC element has a (trip) function of abruptly increasing a resistance when the element itself generates heat to reach a predetermined temperature in case that an overcurrent flows, and if the battery is erroneously short-circuited, the PTC element trips to block the overcurrent, thus making it possible to inhibit abnormal heat generation of the battery.
However, the above described configuration may have some problems. That is, when a large current is almost continuously consumed in a normal use state such as continuous light emission in a stroboscope or continuous photographing in a digital still camera, a PTC element may act as a resistor and may gradually generate heat to unintentionally actuate the PTC element.
It is desirable to actuate the PTC element at the lowest possible temperature at the time of a short circuit, but it is difficult to have a good balance between the heat generation temperature and the actuation temperature of the PTC element in terms of design of a battery. Therefore, there were many cases where heat generation in the battery resulting from an overcurrent at the time of a short circuit was not sufficiently inhibited so that a user feels that a body portion of the battery is hot.
There were cases where heat generation in the PTC element itself when tripped by an overcurrent at the time of a short circuit thermally damaged a resin sealing body covering the PTC element, and the resin sealing body was thermally deformed or carbonized at a high temperature to deteriorate the sealing characteristic of the battery, thus causing liquid leakage.
Thus, one aspect of the invention solves the problems of conventional techniques described above, and provides a highly reliable battery of which the surface temperature of a body portion of a battery at the time of a short circuit is controlled to be low.